A scanning electron microscope as a mode of a charged particle beam apparatus is an apparatus that converges a primary charged particle beam accelerated and emitted from a charged particle source using an electromagnetic lens and detects a secondary signal obtained from a sample when the surface of the sample is irradiated with the primary charged particle beam by electromagnetic deflection while scanning to convert the secondary signal into an image. The scanning electron microscope using an electron source as a charged particle source is widely known as a representative apparatus in this mode and fine shapes can be observed by converging a primary electron beam diminutively and so is used for dimensional measurement and the like of fine circuit patterns in a semiconductor manufacturing process.
The secondary signal obtained when the sample is irradiated with a primary electron beam is a signal having various levels of energy such as secondary electrons and reflected electrons. By selecting and detecting energy of the secondary signal, an image having desired information can be acquired. In an optical system in which a secondary signal travels onto an optical path of primary electrons and a detector to detect the secondary signal is arranged outside an axis of the optical path of primary electrons, it is necessary to deflect the secondary signal without deflecting the primary electron beam.
As a means for implementing this, an apparatus using a Wien filter as a deflecting means of the secondary signal is described in PTL 1. In PTL 1, correcting changes of a curvature of field due to changes of a deflection angle of a primary electron beam by a magnetic pole of an objective lens and causing deflection color aberration using an E×B separator is described.
Also, an apparatus that suppresses a curvature of field as geometric aberration and astigmatism is described in PTL 2. In PTL 2, correcting a curvature of field and astigmatism caused by a Wien filter operating as a deflection color aberration correcting element inside the deflection color aberration correcting element is described.